1. Field of the Invention
The present invention generally relates agricultural machinery having an internal combustion engine. More specifically, the invention relates to agricultural tractors and a system for controlling the RPM of a power take-off used to drive removable agricultural implements, such as soil or bale presses.
2. Description of Related Art
Existing state of the art agricultural tractors are equipped with an internal combustion engine which provides locomotion through the tractor wheels, and it drives external accessories such as bale presses through a power take-off (PTO) on the tractor. A PTO transmission, with several operator selectable steps, connects the engine to the PTO and is used to regulate the RPM of the PTO at a given engine RPM.
The external accessories connected to the PTO are usually designed to be operated at a specific RPM. Therefore, in order to ensure proper operation of the external accessories and to prevent damage due to excessively high RPMs, it is useful to provide an automatic limit to the RPM of the PTO. Consequently, since the RPM of the PTO is directly proportional to the RPM of the tractor engine, this also necessitates limiting engine RPM.
In tractors currently produced by the applicant, engine RPM is adjusted using a pedal or a throttle hand lever. In addition, a limiting potentiometer is provided which permits the operator to set a maximum engine RPM. To set the limiting potentiometer, the operator accelerates the engine until a tachometer indicates the desired RPM and then manually sets the potentiometer. Thereafter, if the engine RPM reaches the limit set on the potentiometer an engine speed control intervenes and prevents the engine from exceeding that limit, regardless of the operator input.
However, this configuration means that the potentiometer limit is based solely on the RPM of the engine and not the PTO RPM. Thus, should conditions require the operator to select a different PTO transmission step, a new set-up of the limiting potentiometer is required. This is a significant disadvantage for existing tractors since the above procedure for adjusting the potentiometer is cumbersome and requires the operator to manually set the appropriate engine RPM, with the engine running, in each case. A further disadvantage is that it is not desirable to limit engine RPM while driving on a road or in the turn-around areas at the ends of fields.
In U.S. Pat. No. 6,607,466 a tractor is described where the nominal RPM of the PTO is preset by a lever calibrated to the desired PTO speed ranges. A controller then regulates the Tractor engine RPM in order to achieve the RPM desired at the PTO. However, unlike the present invention, this is done without a multi-gear transmission between the engine and the PTO. Furthermore, it is not possible for the operator to set the RPM of the engine separately from the PTO.
In U.S. Pat. No. 6,942,595, it is proposed to measure the RPM of the PTO at the outlet of a variable transmission and to use it for regulating the RPM of the engine. In this case an expensive variable transmission is used and again the operator does not have the ability to preset the RPM of the engine.
In view of the above, it is apparent that there exists a need to improve agricultural tractors with a PTO driving external accessories. The objective of this invention is therefore to allow an operator to set both the engine RPM and a maximum PTO RPM without the need to reset the limits whenever a different PTO transmission gear is selected.